In the fueling of aircraft it is necessary to form a grounding connection between the aircraft and the fueling apparatus. Otherwise, a charge of static electricity can build up, leading to an electrical arc or spark discharge. This can cause ignition of the fuel, resulting in damage to the equipment and injury or death of personnel.
At the present time, the grounding of an aircraft during fueling is accomplished using a plug comprising an elongate cylinder formed from electrically conductive metal and having a terminal groove surrounding its distal end. The plug is received in a receptacle mounted on the aircraft which comprises a brass fitting having a beryllium copper spring staked or riveted thereto. The spring is in the form of a hook and includes a rounded tip adapted for engagement with the terminal groove of the plug to form an electrical and mechanical connection between the plug and the receptacle.
It has been found that the present receptacle design incorporates a number of highly disadvantageous characteristics. First, the beryllium copper spring forms an electrical connection with the plug by means of a single point contact. If disengagement between the spring and the plug should occur for any reason, for example, due to vibration or otherwise, an electrical arc can form resulting in ignition of the fuel.
Other disadvantages result from the use of dissimilar metals to form the component parts of the receptacle. Such dissimilar metal construction can lead to increased electrical resistance. Also, because of its two-piece construction, the receptacle is subject to damage if excessive torque is used during installation. Still another disadvantage inherent in the present design involves the fact that only a limited amount of mechanical force can be applied through the beryllium copper spring against the plug which can lead to increased electrical resistance at the point of contact between the spring and the plug.
The present invention comprises an aircraft grounding receptacle which eliminates the foregoing and other problems long since associated with the prior art. In accordance with a first embodiment of the invention, an aircraft grounding receptacle is machined from a unitary length of bar stock comprising an electrically conductive material. The receptacle includes a connecting portion and a tubular portion extending from the connecting portion to a flange situated at the opposite end of the receptacle. A passageway extends through the receptacle to reduced diameter portions situated adjacent to the flange and adapted to matingly receive the terminal groove of an aircraft grounding plug. Four slots extend into the tubular portion from the flange to permit the segments of the tubular portion to flex outwardly to receive and grip the grounding plug.
In accordance with a second embodiment of the invention, an aircraft grounding receptacle is likewise machined from a unitary length of bar stock comprising an electrically conductive material. The receptacle includes a plug receiving portion and a collet portion. The plug receiving portion of the receptacle includes a flange comprising a first surface extending perpendicularly to the axis of the receptacle and a second surface which slopes toward the collet portion. The plug receiving portion further includes an extension which projects through an aperture formed in an aircraft panel when the first surface of the flange engages the interior surface of the panel. The collet portion includes a reduced diameter section adapted to matingly receive an aircraft grounding plug and is provided with four longitudinally extending slots which allow the reduced diameter portion to expand outwardly to matingly receive the distal end of the plug. The exterior of the receptacle is threaded to receive a housing which surrounds the collet portion. A washer is captured between the second surface of the flange and the housing and is secured to the panel of the aircraft by rivets.
The use of the present invention results in numerous advantages over the prior art. First, when an aircraft grounding plug is received in a receptacle incorporating the present invention, a total of eight contact points are established between the receptacle and the plug. This eliminates the possibility that a single point contact will somehow become disengaged, leading to spark discharge. Second, the grounding plug is gripped by four contact tines arranged in two opposed groups, thereby substantially eliminating the possibility of disengagement between the plug and the receptacle. Third, substantially greater mechanical contact pressure between the plug and the receptacle is achieved by means of the invention, which in turn reduces the electrical resistance between the plug and the receptacle. Finally, the present invention comprises a one-piece construction. This provides a receptacle which is capable of withstanding up to twenty times as much mechanical torque as is the case with prior designs, while simultaneously eliminating the problem of increased electrical resistance which can result when dissimilar metals are used in fabricating a grounding receptacle.